It is generally assumed that the primary response of the rat flash evoked potential (FEP) is activated by a retino-geniculate pathway, and that the second response reflects input to the cortex by way of the superior colliculus (SC) or other brainstem structures. In the present study, Male Long Evans rats were implanted with monopolar screw electrodes over the left visual cortex, and a pair of monopolar depth electrodes in each SC, which were used to produce electrolytic lesions. One half of the animals did not receive the electrolytic treatment (controls). FEB waveforms were obtained from all animals prior to treatment, and 2 and 5 days after treatment. Histological analysis was performed to verify electrode placement and determine lesion size. Electrolytic lesions which resulted in massive destruction of the SC produced no decrement in any portion of the rat FEP, but did produce an increase in amplitude of the N2P3 component. The data show that the secondary response of the rat FEP is not generated by SC, but that SC may modulate amplitude of the response.